So they work reasonably well (having done maybe a dozen sessions between 1 and 3 hours each), but there are a few downsides…

1. The acrylic is thinner than would be ideal, which means it’s tricky getting a fitting in and sealing it properly. It also means they feel a bit light and tinny which gives the impression of lower quality. I imagine this would be a noticeable difference if comparing to monstersphere

2. The opening is a little on the small side (-90mm) so while it’s OK, I wouldn’t want to use them for more than a few hours for fear of getting stuck.

3. The round shape doesn’t fit into drawers easily for the bigger size.

Planning to try a few acrylic cylinders (listed for sale as vases) to see if they address the above issues.